MOSS Set Advanced Permission - Object Reference not set

Hey guys,

I had an strange behaviour in one of our customers portals.

Today the customer told me, that when he try to access the Advanced Permission Page of a Site in SharePoint he get an error:

Object reference not set to an instance of an object.   at Microsoft.SharePoint.SPSite.get_IISAllowsAnonymous()
   at Microsoft.SharePoint.ApplicationPages.UserRoles.InitPage()
   at Microsoft.SharePoint.ApplicationPages.CBaseAclPage.OnLoad(EventArgs e)
   at System.Web.UI.Control.LoadRecursive()
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

After some research I found a blog post which will describe the behaviour and how to fix it.

Many Thanks to Dan Lewis who has spent time on this error!!

There are several resolutions for this error described in the post above.

In my case the Authentication Provider of the WebApp was completly deleted.

So I have to extend the WebApp with a new Authentication Provider.

greets